My Cub sprung a leak the other day right after I started it up. My suspicion is the gasket where the radiator mounts to the front casting. After we had the tractor painted several years ago, I reinstalled the radiator, used the cork gasket and some Form A Gasket (flexible kind) but apparently that didn't hold up as well as I hoped. Here are a couple of questions:

1. The front casting surface where the radiator flange mounts has somewhat of a crown to it. Is that normal? I'm thinking about doing some careful grinding to reduce it somewhat. I can provide some pictures if needed. At some point in the tractor's life, the casting had a crack that was welded up. The weld seems to be holding find. Across the width of the casting, the center is 1/4" higher than the ends.

2. The leak appeared to be at the gasket, but it was a little hard to pinpoint exactly where. When you reinstall the cork gasket, do you normally give it some help with silicone or Form A Gasket?

3. Since I have the radiator off, has anyone got a good way to pressure test it? I can fabricate a plate at work to seal off the bottom and put a couple of pounds of air in it and see if it leaks.

4. Since the radiator is off and I don't know how old it is, should I just go ahead and spend the money on a new one. They're a couple of hundred bucks, but that would at least eliminate an unknown and a possible failure later on (or sooner).

My preferred route would be to take it to a Radiator and Gas Tank Repair shop ... but I guess you already have that covered. So, the next preferred route would be to follow the master's advice - How To Test a Radiator

Also, I do not use Form-a-Gasket or silicone on the cork gaskets. I tend to use Hi-Tack to keep the gasket in place during reassembly but that would be about it.

Thanks for all the tips. I like the base plate for testing the radiator shown in the "how to test a radiator". I've got access to MDF and aluminum so it shouldn't be too hard to make. If I find a leak I'll take it to a shop and see if they can repair it. Regarding the hump, has anyone seen this before? I looked at the thickness of the casting and there is some material, but not a lot that can be removed to lessen the crown. I would really like to avoid having to purchase a front casting.

Most likely your bolster has been frozen (water, no antifreeze), which has caused the bulge. Your radiator will have a matching bend to it. When installing a radiator, I always use a new gasket with a very thin layer of the silicone form a gasket on each side. if you go to the How TO section there are some procedures for testing for leaks.

If you are keeping the old bolster, do not try to straighten the bottom of the radiator when you test it or have it repaired. You will need the bow in the radiator to match the bolster. Also keep in mind that the older Cubs do not need a pressurized cooling system, which makes repairing the radiator and any cracks in the bolster less of a challenge.

danovercash wrote:Replace the bolster, not the radiator, JMHO. Especially if radiator checks good.

I agree, replace the bolster. I had one, that was bulged so much, the PO had to enlarge the hole in the hood, to place the hood on. Bulge is from freezing, as was mentioned. Never understood, why the bolster and head crack, from freezing, and the radiator survives? Ed

I don't believe new ones are available, if they were I'm sure they'd be a ridiculous amount of money. If you do change the bolster (I would in your case) it gives you a great opportunity to check/fix things, like the front seal on the engine and seals in the steering assembly. ...which by the way is a slippery slope, once you start "fixing things" where do you stop???? I ended up rebuilding the engine "while it was apart"! ...and I should/could have kept going. Going from front to back I chose to stop at the rear main bearing. Maybe this winter I'll start at the back and go forward ...or maybe not!

I cleaned off the surface of the front casting and found some more troubling signs:

1. The front surface where the radiator bolts on has a pretty good wrinkle in it. As I mentioned, it was welded in the past and it's probably done.2. On that front surface, I noticed a faint line that appears to be another crack3. On the inside of the casting, where bosses are cast in place for the blind tapped holes for the radiator flange, one boss has one side that has cracked away leaving a path past the threads. This is where I think the leak started showing.

So it looks like I'll need another front casting and I'm probably going to replace the radiator as well. So here are my questions:

1. What's the best way to support the tractor while removing the front casting? It looks like the front end is supported by the underside below the steering gear. I'm assuming I probably need to bolt to the bosses on the side of the engine rather than place blocks under the oil pan.2. Since I'll be pulling the steering gear apart, what seals and other items will I need?3. Is the front crank seal pretty much a pull and replace job?4. As far as sourcing a new casting, I see Steiner has one but it's around $360. Are there other sources? I'm in the Atlanta area. What's a decent price on a front casting?5. Any other tips or tricks?

I'll be looking through my PDF manuals as well, but it's always good to ask before tearing into something.